Sheet stacking apparatus, image forming system, and image forming apparatus

ABSTRACT

A sheet stacking apparatus includes a conveying unit that stacks sheet stacks while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point based on various conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and incorporates by reference the entire contents of Japanese priority document 2007-323501 filed in Japan on Dec. 14, 2007 and Japanese priority document 2008-251137 filed in Japan on Sep. 29, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet stacking apparatus, an image forming system, and an image forming apparatus.

2. Description of the Related Art

Recently, an image forming system can provide various types of post-processing on an image-formed sheet, and particularly, an image forming system capable of producing so-called saddle-stitched booklet has been increasing. The saddle-stitched booklet is produced by stapling a stack of sheets at its center and then folding the stapled sheet stack in half. The saddle-stitched booklet is discharged and stacked without any further processing or after a fore edge thereof is cut by a cutting apparatus called a trimmer. In the saddle stitching, sheets are conveyed in a path different from that for other stapling processing such as stapling an end of sheets, and the saddle-stitched booklet is discharged from a discharge port provided exclusively therefor in most cases. Because the saddle-stitched booklet is produced by folding a stapled sheet stack in half, or by stapling at its center stacked sheets that are folded in half, the booklet tends to become large in volume. For this reason, the saddle-stitched booklets are difficult to be stacked vertically unlike in the case of booklets produced by stapling an end of a stack of sheets. Therefore, the saddle-stitched booklets are often stacked by arranging them in a lateral direction while obliquely shifting them little by little.

Such a technology is disclosed, for example, in Japanese Patent Application Laid-open No. 2007-119089, in which a booklet stacking apparatus includes a discharge unit that discharge a plurality of booklets sequentially, a conveying unit that conveys the booklets while arranging them in a partially overlapped manner, a stacking unit in which the booklets are stacked, and a conveying control unit that controls a feed amount per booklet in the conveying unit in accordance with the amount of the booklets to be stacked.

However, in the above technology, a shift stacking cannot be employed unlike in the case of stapling an end of a stack of sheets, so that, for example, when the saddle-stitched booklets for a plurality of jobs are produced from sheets of the same size and sequentially stacked, it is difficult to distinguish the booklets of each job. FIG. 9 is a schematic diagram illustrating a conventional example of a saddle-stitched booklet stacked state on a stacking tray, in which a cutting apparatus 111 and a stacking tray 112 are viewed from above. As shown in FIG. 9, when booklets 25 of the same size are sequentially stacked on the stacking tray 112, it is difficult to distinguish the booklets 25 of each job. Therefore, when sorting the booklets 25 for each job, a user needs to check each of the booklets 25 to recognize a transition point of each job. This results in requiring useless time for sorting, thereby causing a problem in workability after discharging the booklets.

SUMMARY OF THE INVENTION

It is an object of the present invention to at least partially solve the problems in the conventional technology.

According to an aspect of the present invention, there is provided a sheet stacking apparatus including a conveying unit that stacks sheet stacks while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point.

According to another aspect of the present invention, there is provided an image forming system including an image forming apparatus that forms an image on a sheet; a sheet processing apparatus that receives a plurality of sheets from the image forming apparatus, stacks a plurality of the sheets in a sheet stack, and performs a saddle-stitching and a center-folding on the sheet stack; and a sheet stacking apparatus that includes a conveying unit that stacks sheet stacks processed in the sheet processing apparatus while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point.

According to still another aspect of the present invention, there is provided an image forming apparatus including a sheet stacking apparatus including a conveying unit that stacks sheet stacks while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point.

The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an image forming system according to an embodiment of the present invention;

FIG. 2 is a block diagram of a control configuration of a cutting apparatus of the image forming system;

FIG. 3 is a schematic diagram illustrating an example of a saddle-stitched booklet stacked state on a stacking tray shown in FIG. 1;

FIG. 4 is a schematic diagram of a mechanical configuration of the cutting apparatus and the stacking tray;

FIG. 5 is a plan view of the cutting apparatus and the stacking tray;

FIG. 6 is a flowchart of an operation procedure of the cutting apparatus and the stacking tray;

FIG. 7 is a schematic diagram of a liquid crystal display screen of an operation panel shown in FIG. 1;

FIG. 8 is a schematic diagram of a finisher shown in FIG. 1; and

FIG. 9 is a schematic diagram illustrating a conventional example of a saddle-stitched booklet stacked state on a stacking tray;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Exemplary embodiments of the present invention are explained in detail below with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an image forming system according to the present embodiment of the present invention. The image forming system includes an image forming apparatus 1, an inserter 3, a sheet folding apparatus 6, a binding apparatus 7, a post-processing apparatus (finisher) 9, and a cutting apparatus 11.

The image forming apparatus 1 is a digital multi-function peripheral (MFP), and includes an automatic document feeder (ADF) 2 and an operation panel 20 with a liquid crystal display 20 b. The image forming apparatus 1 is connected to the inserter 3 on the downstream side in a direction in which a sheet-like recording medium (hereinafter, “sheet”) is conveyed. The inserter 3 includes sheet trays 4 and 5, and can insert a sheet on which an image is formed or a sheet that cannot pass the image forming apparatus 1 independently, or over and under a sheet output from the image forming apparatus 1 or between any sheets.

The sheet folding apparatus 6 capable of folding a sheet in various ways such as Z-fold and tri fold is connected to the downstream side of the inserter 3. The binding apparatus 7 is connected to the downstream side of the sheet folding apparatus 6. The binding apparatus 7 is, for example, a tape binding apparatus, a ring binding apparatus, or a case binding apparatus. A booklet bound by the binding apparatus 7 is delivered to a binding tray 8. The finisher 9 is connected to the downstream side of the binding apparatus 7. The finisher 9 includes a punching device and a stapling device therein, enabling to perform punching and stapling. The finisher 9 also has a function for producing a saddle-stitched booklet. Sheets or booklets of which ends are stapled are discharged onto a post-processing tray 10.

The cutting apparatus 11 is arranged further on the downstream side of the finisher 9. The cutting apparatus 11 receives a saddle-stitched booklet from the finisher 9 and cuts a fore edge of the booklet for aligning. The booklet with its fore edge cut is discharged onto a stacking tray (post-processing tray) 12 to be stacked thereon.

FIG. 2 is a block diagram of a control configuration between the cutting apparatus 11 and the image forming apparatus 1. The cutting apparatus 11 includes a control device 95 that consists of a microcomputer including a central processing unit (CPU) 96 and an input/output interface (I/O I/F) 97, and a signal from each sensor or each switch of the operation panel 20 is input to the CPU 96 from a control circuit of the image forming apparatus 1. Data on detection by various sensors in the cutting apparatus 11 is also input to the CPU 96 via the I/O I/F 97. The image forming system is operated by inputting instructions from the operation panel 20, i.e., the image forming system is controlled based on the operation information from the operation panel 20. If each apparatus of the image forming system is used independently, for example, an operation panel 21 can be provided to the finisher 9 separately from the operation panel 20 of the image forming apparatus 1, and an operation for stacking sheets can be controlled based on the operation information from the finisher 9.

The CPU 96 drives driving elements (not shown) of the cutting apparatus 11 and displays necessary information based on the operation information input from the image forming apparatus 1. Each of the inserter 3, the sheet folding apparatus 6, the binding apparatus 7, and the finisher 9 on the upstream side of the cutting-apparatus 11 also has the same control device as that of the cutting apparatus 11, and each control device is connected to the apparatuses on upstream and downstream sides via a transmit data (TXD) terminal and a receive data (RXD) terminal for data communication. With this configuration, each of the apparatuses 3, 6, 7, 9, and 11 connected to the image forming apparatus 1 on the downstream side can be controlled from the image forming apparatus 1. The image forming apparatus 1 and each of the apparatuses 3, 6, 7, 9, and 11 are controlled in the following manner. That is, a CPU mounted on each of the apparatuses 3, 6, 7, 9, and 11 loads a computer program written in a read only memory (ROM) (not shown) into a random access memory (RAM) (not shown), and executes the computer program while storing necessary data into the RAM.

FIG. 3 is a schematic diagram illustrating an example of a saddle-stitched booklet stacked state on the stacking tray 12, in which the cutting apparatus 11 and the stacking tray 12 are viewed from above. Even when the booklets 25 of the same size are stacked on the stacking tray 12, an interval W is provided between the booklets 25 every time a job is switched, so that a user can easily determine a job transition point where a job is switched.

FIG. 4 is a schematic diagram of a mechanical configuration of the cutting apparatus 11 and the stacking tray 12 connected to the cutting apparatus 11, and FIG. 5 is a plan view of the cutting apparatus 11 and the stacking tray 12.

In the image forming system, sheets fed from the image forming apparatus 1 or the inserter 3 are saddle stitched and center-folded, i.e., folded in half, as a stack of sheets by the finisher 9 to be formed into the booklet 25. The booklet 25 is discharged from the finisher 9 with its back side (folded side) directed forward. The cutting apparatus 11 is arranged adjacent to the lower stage of the finisher 9, and receives the booklet 25 from the finisher 9.

The cutting apparatus 11 includes a feeding unit 31, a positioning unit 44, a cutter unit 41, and a tray unit 54.

The feeding unit 31 includes an entrance guide plate 32, upper and lower feeding guides 33 and 34, a carrying-in sensor 35, and a feeding-side conveying motor 36. The saddle-stitched booklet 25 is delivered to the feeding unit 31 from the entrance guide plate 32, and is conveyed therein while being nipped between the feeding guides 33 and 34. The feeding guide 34 is a belt having a substantially round cross section, and the feeding guide 33 under the feeding guide 34 is a flat belt. The feeding guide 34 swings around its fulcrum on the entrance side, so that the gap between the feeding guides 33 and 34 can be changed depending upon the thickness of the booklet 25, enabling to cope with booklets with various thicknesses.

The positioning unit 44 includes a conveying mechanism 44 a, an end stopper 44 b, and a claw 44 c. The positioning unit 44 further includes a positioning-side entrance-roller pressing motor 45, a positioning-side entrance-roller pressure sensor 46, a positioning home position (HP) sensor 47, a claw pressing motor 48, a stopper HP sensor 49, a claw moving motor 50, a claw sheet sensor 51, a positioning-side sheet discharge motor 52, and a discharge sensor 53 in association with the driving of the conveying mechanism 44 a, the end stopper 44 b, and the claw 44 c.

The booklet 25 is conveyed from the feeding unit 31 to the positioning unit 44. The conveying mechanism 44 a includes a flat belt that is the same as, the feeding guide 33, and the end stopper 44 b located on the upper side in the positioning unit 44 is movable for adjusting the size or the cutting width of the booklet 25. The claw 44 c is prepositioned in accordance with the information such as the size and the cutting position of the booklet 25 transmitted from the image forming apparatus 1, and the booklet 25 is conveyed to cause the back thereof to be brought into contact with the claw 44 c, so that the cutting position of the booklet 25 is determined. The positioning unit 44 further includes a pressing mechanism including the claw pressing motor 48, by which the booklet 25 after being positioned is pressed to be flattened, whereby the booklet 25 is ready to be cut.

The cutter unit 41 is arranged between the feeding unit 31 and the positioning unit 44. The cutter unit 41 is a guillotine cutter including a movable upper blade having an edge forming an acute shearing angle and a fixed lower blade having an edge forming an obtuse angle (about 90 degrees). After the positioning unit 44 determines the cutting position of the booklet 25, the upper blade of the cutter unit 41 is driven to move down by a cutter motor 42, thereby cutting the booklet 25. The cutter unit 41 includes a pressing mechanism. The pressing mechanism presses one side of the booklet 25 near the cutting position before the upper blade starts to move down for cutting, and thereafter the upper blade moves down and cut the booklet 25. Therefore, the booklet 25 is prevented from being displaced at the time of cutting. As shown in FIG. 4, the cutting apparatus 11 includes a cutter HP sensor 43 that detects a home position of the cutter.

Cut waste generated by cutting a sheet by the cutter unit 41 falls into a waste box 37 arranged under the cut position by gravity. The waste box 37 is provided with a sensor 38 for detecting that the waste box 37 is full of cut waste and a sensor 39 for detecting that the waste box 37 is set.

The tray unit 54 includes discharge levers 55, a first full-state sensor 56, a second full-state sensor 57, a remaining sheet sensor 58, and a conveying motor 59. The booklet 25 with its fore edge cut is released from the pressure by the pressing mechanism, is conveyed to a discharge portion by a conveying mechanism on the lower side of the positioning unit 44, and is discharged onto the stacking tray 12 by a discharge roller (not shown). A pair of flat belts 24 and a driving mechanism (not shown) for the flat belts 24 are provided to the stacking tray 12 to convey and align the booklets 25 stacked on the stacking tray 12. Every time the booklet 25 is discharged from the cutting apparatus 11, the flat belts 24 move by a predetermined feed amount to convey the booklets 25 on the stacking tray 12 little by little. It is possible to change the feed amount by the flat belts 24 depending upon the size or the thickness of the booklet 25, enabling to adjust an overlapping length of the booklets 25, which results in keeping the booklets 25 stacked on the stacking tray 12 in a proper posture and stacking a large number of the booklets 25 on the stacking tray 12. In FIG. 5, a pair of the flat belts 24 is used, however, a flat belt having a wide width or three or more flat belts can be used instead. If the number of belts is large, any type of belt can be used instead of the flat belt so-long as the booklets 25 can be conveyed in a partially overlapping state.

The second full-state sensor 57 is provided to the discharge levers 55 arranged in a discharge entrance portion, which detects the amount of sheets discharged from the cutting apparatus 11 by detecting a rotation angle of the discharge levers 55. The second full-state sensor 57 can detect a full state of the booklets 25 on the stacking tray 12 together with the result of the detection by the first full-state sensor 56 provided near the end of the stacking tray 12. Specifically, after the first full-state sensor 56 is turned on, when the tray unit 54 detects that the discharge levers 55 rotate by a predetermined angle, a full-state signal is output.

In addition to the feed amount (booklet interval) by the flat belts 24 between the booklets 25 in a job, the feed amount (job interval) by the flat belts 24 between consecutive jobs can also be changed in accordance with a signal transmitted from the image forming apparatus 1, thus enabling to adjust an interval of the booklets 25 between jobs, i.e., an interval between conveyance of the last booklet 25 of one job and that of the first booklet 25 of a subsequent job. Therefore, it is possible to determine the job transition point where a job is switched on the stacking tray 12.

FIG. 6 is a flowchart of an operation procedure of the cutting apparatus 11 and the stacking tray 12. In the present embodiment, if a size of the booklets 25 in a job is different from that in the previous job, the flat belts 24 basically do not move by the job interval even between the consecutive jobs. In other words, in the above case, every time the booklet 25 is discharged, the flat belts 24 move by the booklet interval even between the jobs. Then, when the last booklet 25 of the jobs is discharged, the flat belts 24 move by the job interval in accordance with the setting conditions. However, a user can select the setting for moving the flat belts 24 by the job interval between the consecutive jobs in the above case.

Specifically, when a job is started in a saddle-stitching mode, the image forming apparatus 1 starts printing (Step S101). When printed sheets are delivered to the finisher 9, sheet alignment and saddle stitching are performed on a stack of the printed sheets (Step S102). Then, the saddle-stitched sheet stack is delivered to the cutting apparatus 11, in which a fore edge of the saddle-stitched sheet stack is cut by the cutter unit 41 thereby producing the booklet 25 (Step S103). Thereafter, the booklet 25 is discharged to the tray unit 54 by the conveying mechanism (Step S104).

The operations from Steps S101 to S104 are repeated, and when the last booklet 25 of the job is discharged (YES at Step S105), instruction data from the image forming apparatus 1 is checked to determine whether it is set to provide the job interval between consecutive jobs (Step S106). When it is determined NO at Step S106, the job interval is not provided between the jobs. When it is determined YES at Step S106, it is further checked whether the size of the booklets 25 in the previous job is the same as that in the present job based on the data from the image forming apparatus 1 (Step S107). If the size of the booklets 25 is different between the jobs (NO at Step S107), the job interval is not provided between the jobs because the booklets 25 can be distinguished between the jobs. If the size of the booklets 25 is the same between the jobs (YES at Step S107), it is further checked whether the instruction data from the image forming apparatus 1 is a setting for providing the job interval between the jobs (Step S108). If the setting is not for providing the job interval (NO at Step S108), the job interval is not provided between the jobs. If the setting is for providing the job interval (YES at Step S108), the flat belts 24 are moved by the job interval (Step S109). Thereafter, the booklet 25 for the next job is discharged onto the stacking tray 12 in a state where there is the interval W from the last booklet 25 in the previous job as shown in FIG. 3.

The job interval (feed amount of the booklet 25) is set, for example, based on a computer program in the image forming apparatus 1 or a value input using a ten key 20 a of the operation panel 20 shown in FIG. 1, and the set job interval data is transmitted to the cutting apparatus 11 as a signal. In the cutting apparatus 11, the control device 95 controls the conveying motor 59 for the tray unit 54 so that the booklets 25 are conveyed to have the job interval. A user can set whether to change the feed amount from the operation panel 20. Specifically, as shown in FIG. 7, it is set such that a user can input the instruction by, for example, pressing a sort/shift key 20 c for post-processing on a display screen of the liquid crystal display 20 b.

When it is set to have the booklet interval between the jobs, if the size of the booklets 25 is different between the jobs, the job transition point can be easily recognized, so that the feed amount is not changed. In the same manner, if the number of sheets of the booklet 25 is different between the jobs, the feed amount is not changed. Therefore, a larger number of the booklets 25 can be stacked. The image forming apparatus 1 recognizes the sheet size and the number of the sheets of the booklet 25, so that even if a user inputs an instruction for changing the feed amount from the operation panel 20, the control device of the image forming apparatus 1 is controlled not to transmit a signal for instructing a feed amount changing to the control device 95. That is, the feed amount is controlled not to be changed by causing the signal for instructing the feed amount changing not to be transmitted.

If a user wants to handle one job independently, it is set such that after the last booklet 25 of the job is discharged onto the stacking tray 12, the booklets 25 of the job are conveyed to the position where the first full-state sensor 56 detects that the stacking tray 12 is in a full state to be handled as the full state. When the stacking tray 12 is in the full state, the process is stopped and the full state is notified to a user. Therefore, when a user wants to handle one job independently, the user can take only the booklets 25 of the desired job on the stacking tray 12 through the stop operation and the notification. Thus, because the booklets 25 are not mixed with those of other jobs, workability can be improved.

FIG. 8 is a schematic diagram of the finisher 9. The finisher 9 is attached to the side of the binding apparatus 7, and a sheet discharged from the image forming apparatus 1 passes conveying paths provided on the upper portions of the apparatuses downstream of the image forming apparatus 1 to be conveyed to the finisher 9. The sheet passes a conveying path A including a post-processing unit (in the present embodiment, a punching unit 451) that performs post-processing on a sheet, and is conveyed to a conveying path B for guiding the sheet to an upper tray 453, a conveying path C for guiding the sheet to a shift tray 454, or a conveying path D for guiding the sheet to a processing tray F (hereinafter, also referred to as “staple processing tray”) for performing aligning, stapling, and the like by branching claws 315 and 316.

Sheets that are guided to the staple processing tray F via the conveying paths A and D are aligned and stapled. The stapled sheet stack is guided to the conveying path C or a processing tray G (hereinafter, also referred to as “center-folding tray”) for folding the stapled sheet stack and the like by a branching guide plate 354 and a movable guide 355 as a deflecting unit. The sheet stapled that is center-folded in the center-folding tray G is guided via a conveying path H to the cutting apparatus 11. A branching claw 317 is provided in the conveying path D, which is held in the state as shown in FIG. 8 by a low-load spring (not shown). After a trailing end of a sheet passes the branching claw 317, the sheet is conveyed backward along a pre-stack roller 308 by reversely rotating at least a pair of conveying rollers 309 out of the conveying rollers 309, a pair of conveying rollers 310, and a pair of staple sheet discharge rollers 311. The trailing end of the sheet is guided to a sheet storing unit E to hold up the sheet in the sheet storing unit E. This makes it possible to stack the next sheet on the sheet and convey both the sheets in an overlapped manner. It is also possible to stack and convey two or more sheets in an overlapped manner by repeating this operation.

In the conveying path A to which the conveying paths B, C, and D are commonly connected on the upstream side thereof, a sheet entrance sensor 401 that detects a sheet received from the side of the image forming apparatus 1 is arranged. Moreover, on the downstream of the sheet entrance sensor 401, an entrance roller 301, the punching unit 451, a punching-waste hopper 452, a pair of conveying rollers 302, the branching claw 315, and the branching claw 316 are sequentially arranged. The branching claws 315 and 316 are retained in the state shown in FIG. 1 by springs (not shown). When a solenoid (not shown) is turned on, the branching claws 315 and 316 rotate upward and downward, respectively, to convey the sheet to the conveying path B, C, or D.

The finisher 9 is capable of applying various kinds of processing to sheets such as punching (using the punching unit 451), aligning and end-face stapling, i.e., stapling an end face (using jogger fences 353 and an end-face stapler S1), aligning and saddle stitching (using the jogger fences 353 and a saddle-stitching stapler S2), sorting (using the shift tray 454), and center folding (using a folding plate 374 and a pair of folding rollers 381).

A shift-tray sheet discharge unit located on the most downstream section of the finisher 9 includes a pair of shift sheet discharge rollers 306, a return roller 313, a sheet surface sensor 403, the shift tray 454, a shift mechanism, and a shift tray elevating mechanism. The shift mechanism and the shift tray elevating mechanism perform a shift operation and a tray lifting and lowering operation. The return roller 313 made of sponge comes into contact with a sheet discharged from the shift sheet discharge rollers 306 to strike a trailing end of the sheet against an end fence thereby aligning the sheet. The return roller 313 is rotated by torque of the shift sheet discharge rollers 306. A tray-rise limit switch is provided near the return roller 313. When the shift tray 454 rises to push up the return roller 313, the tray-rise limit switch is turned on to stop a tray elevating motor. Thus, the shift tray 454 is prevented from overrunning. The sheet surface sensor 403 as a sheet-surface position detecting unit for detecting a position of a surface of a sheet or a sheet stack discharged onto the shift tray 454 is provided near the return roller 313.

Sheets discharged by the staple sheet discharge rollers 311 are sequentially stacked on the staple processing tray F. Every time a sheet is stacked on the staple processing tray F, the sheet is aligned in a longitudinal direction (a sheet conveying direction) by a tapping roller 312 and aligned in a lateral direction (a direction orthogonal to the sheet conveying direction, i.e., a sheet width direction) by the jogger fences 353. The end-face stapler S1 is driven to perform end-face stapling in response to a stapling signal from a control device during the time between jobs, i.e., between the time when the last sheet of the present sheet stack is received and the time when the first sheet of the next sheet stack is received. Immediately thereafter, the end-face stapled sheet stack is conveyed to the shift sheet discharge rollers 306 by a discharge belt 352, from which discharge claws 352 a are projected, and is discharged onto the shift tray 454 set at a position for receiving the sheet stack.

A HP sensor 402 is turned on/off by the discharge claw 352 a, so that the HP sensor 402 detects a home position of the discharge claw 352 a. In the present embodiment, two discharge claws 352 a are arranged on the outer circumferential surface of the discharge belt 352 at oppositely spaced positions, and alternately convey a sheet stack out of the staple processing tray F. The discharge belt 352 and a drive pulley therefor are arranged on a drive shaft of the discharge belt 352 that is driven by a discharge motor (not shown) at its center in the sheet width direction. A plurality of discharge rollers 356 is arranged and fixed symmetrically with respect to the drive pulley. The peripheral speed of the discharge rollers 356 is set to be higher than that of the discharge belt 352.

The tapping roller 312 swings around a fulcrum by a tapping solenoid (SOL). The tapping roller 312 intermittently taps a sheet fed into the staple processing tray F to bring the sheet into contact with a trailing edge fence 351. The tapping roller 312 rotates counterclockwise. The jogger fences 353 are driven by a jogger motor (not shown) capable of rotating reversely via a timing belt and reciprocates in the sheet width direction. The end-face stapler S1 is driven by a stapler-moving motor (not shown) that can run reversely via a stapler-moving timing belt (not shown). The end-face stapler S1 is moved in the sheet width direction to staple a sheet stack at a predetermined end position.

The saddle-stitching stapler S2 is arranged such that the distance between the trailing edge fence 351 and the stapling position by the saddle-stitching stapler S2 is equal to or longer than half of the length of a sheet of the maximum size that cane be saddle-stitched. In the present embodiment, two saddle-stitching staplers S2 are arranged symmetrically with respect to the center for alignment in the sheet width direction to be fixed to a stay. The saddle-stitching stapler S2 has a known configuration, and therefore detailed explanation thereof is omitted. When performing saddle stitching, the jogger fences 353 align the sheets in a direction orthogonal to the sheet conveying direction, and the trailing edge fence 351 and the tapping roller 312 align the sheets in the sheet conveying direction. Thereafter, the discharge belt 352 is driven to lift a stack of the sheets while the discharge claw 352 a supports the trailing end of the sheet stack until the center of the sheet stack is positioned to the stapling position by the saddle-stitching staplers S2. Then, the discharge belt 352 is stopped and the sheet stack is saddle-stitched by the saddle-stitching staplers S2. The saddle-stitched sheet stack is conveyed to the center-folding tray G to be center-folded. As shown in FIG. 8, a sheet sensor 404 is provided that detects a sheet on the staple processing tray F.

In the present embodiment, a sheet stack deviation unit is provided on the most downstream side of the staple processing tray F in the sheet conveying direction, by which the saddle-stitched sheet stack is conveyed from the staple processing tray F to the center-folding tray G to be center-folded.

The sheet stack deviation unit includes the branching guide plate 354 and the movable guide 355. The branching guide plate 354 is provided to be swingable around a fulcrum upwardly and downwardly, and a rotatable pressing roller 357 is provided on the downstream side of the branching guide plate 354. The branching guide plate 354 is pressed toward the discharge rollers 356 by a spring (not shown). The movable guide 355 is supported by the rotation shaft of the discharge rollers 356 to be swingable. The movable guide 355 is driven to swing around the rotation shaft of the discharge rollers 356 by a driving source (not shown), whereby the right side end of the movable guide 355 in FIG. 8 comes into contact with the end of the branching guide plate 354 to form a path along the outer circumferential surface of the discharge rollers 356, through which the saddle-stitched sheet stack is guided to the center-folding tray G.

The finisher 9 includes a control circuit same as that shown in FIG. 2 and is controlled by a CPU.

The finisher 9 has five modes of a non-stapling mode (1), a non-stapling mode (2), a sorting-and-stacking mode, a stapling mode, a saddle-stitching binding mode. In the non-stapling mode (1), sheets are conveyed through the conveying paths A and B to be discharged from the upper tray 453 without stapling. In the non-stapling mode (2), sheets are conveyed through the conveying paths A and C to be discharged from the shift tray 454 without stapling. In the sorting-and-stacking mode, sheets are conveyed through the conveying paths A and C to be discharged from the shift tray 454 while the shift tray 454 shifts in a direction orthogonal to the sheet discharging direction for every set of sheets to sort each set discharged on the shift tray 454. In the stapling mode, sheets are conveyed through the conveying paths A and D to the staple processing tray F, in which the sheets are aligned and end-face stapled, and thereafter, the end-face stapled sheet stack is discharged onto the shift tray 454 through the conveying path C. In the saddle-stitching binding mode, sheets are conveyed through the conveying paths A and D to the staple processing tray F, in which the sheets are aligned and saddle-stitched, thereafter, the saddle-stitched sheet stack is center-folded in the center-folding tray G, and the center-folded sheet stack is discharged onto the lower tray 203 through the conveying path H. In the saddle-stitching binding mode, the branching claws 315 and 316 both are rotated counterclockwise, so that the path from the conveying path A to the conveying path D is opened. Furthermore, the branching guide plate 354 and the movable guide 355 are in the closed state to guide the sheet stack to the center-folding tray G in which the sheet stack is center-folded.

The saddle-stitched and center-folded sheet stack is delivered to the cutting apparatus 11, in which the fore edge thereof is cut to be discharged to the stacking tray 12.

The image forming apparatus 1 is a copier including a scanner as an example, however, can be a printer that does not include a scanner, a digital MFP including a printer function, a copier function, and a facsimile function, or the like.

According to the present embodiment, the feed amount of the booklet 25 on the stacking tray 12 can be changed at the job transition point, so that the booklets 25 between the jobs can be distinguished on the stacking tray 12. Therefore, workability after staking the booklets 25 is improved.

Moreover, the feed amount of the booklet 25 at the job transition point can be changed by a signal from the image forming apparatus 1, so that the present embodiment can be achieved by using a typical hardware configuration. Thus, a high-performance system can be provided without significant cost increase.

Furthermore, the feed amount of the booklet 25 at the job transition point can be changed by a shift-on signal or a sort-on signal from the image forming apparatus 1, so that the present embodiment can be achieved by using a typical hardware configuration and a typical data communication and command configuration. Thus, a high-performance system can be provided without significant cost increase.

Moreover, it is possible to choose whether to change the feed amount of the booklet 25 at the job transition point through operation of the operation panel 20, so that a user can choose a processing method according to a user's preference. Thus, a system can be configured according to a user's preference.

Furthermore, it is possible to choose whether to change the feed amount of the booklet 25 at the job transition point by the sort/shift key 20 c, so that a high-performance system according to a user's preference can be provided without significant cost increase.

Moreover, it is possible at the time of the job transition point to convey the booklets 25 to the position where the first full-state sensor 56 detects a full state of the booklets 25 on the stacking tray 12 to be handled as the full state. Therefore, when the job is finished, the process can be stopped and the full state can be notified to a user. Thus, a system can be configured according to a user's preference.

Furthermore, it is possible to set the feed amount of the booklet 25 at the job transition point from the operation panel 20, so that a user can determine the feed amount of the booklets 25 between jobs. Therefore, the amount of the booklets 25 to be stacked on the stacking tray 12 can be increased or the interval of the booklets 25 between jobs can be increased according to a user's preference. Thus, a system can be configured according to a user's preference.

Moreover, if the size of the booklets 25 or the number of sheets of the booklet 25 is different between jobs, it is possible to choose not to transmit a signal for changing the feed amount of the booklet 25 even when it is set to change the feed amount. Therefore, the amount of the booklets 25 to be stacked on the stacking tray 12 can be increased, and a user can choose a processing method according to a user's preference. Thus, an easier-to-use and higher-performance system can be provided.

According to an aspect of the present invention, workability after taking out saddle-stitched booklets from a stacking tray can be improved.

Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth. 

1. A sheet stacking apparatus comprising: a conveying unit that stacks sheet stacks while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point.
 2. The sheet stacking apparatus according to claim 1, wherein each of the sheet stacks is center-folded.
 3. The sheet stacking apparatus according to claim 1, wherein each of the sheet stacks is saddle-stitched and center-folded.
 4. An image forming system comprising: an image forming apparatus that forms an image on a sheet; a sheet processing apparatus that receives a plurality of sheets from the image forming apparatus, stacks a plurality of the sheets in a sheet stack, and performs a saddle-stitching and a center-folding on the sheet stack; and a sheet stacking apparatus that includes a conveying unit that stacks sheet stacks processed in the sheet processing apparatus while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point.
 5. The image forming system according to claim 4, wherein the feed amount changing unit changes the feed amount based on a signal from the image forming apparatus.
 6. The image forming system according to claim 5, wherein the image forming apparatus includes an operation panel, and the image forming apparatus outputs the signal to the feed amount changing unit indicative of an instruction from the operation panel.
 7. The image forming system according to claim 5, wherein the image forming apparatus includes an operation panel, and the image forming apparatus outputs the signal to the feed amount changing unit indicative of an instruction from the operation panel.
 8. The image forming system according to claim 7, wherein when the feed amount is set to change at the job transition point and when a size of sheets of the sheet stacks are different between jobs, the feed amount changing unit does not change the feed amount.
 9. The image forming system according to claim 7, wherein when the feed amount is set to change at the job transition point and when number of sheets of the sheet stacks are different between jobs, the feed amount changing unit does not change the feed amount.
 10. The image forming system according to claim 8, wherein the feed amount changing unit negates the signal when not changing the feed amount.
 11. The image forming system according to claim 9, wherein the feed amount changing unit negates the signal when not changing the feed amount.
 12. The image forming system according to claim 4, further comprising: a full-state sensor that detects a full state of the sheet stacking apparatus; and a full-state setting unit that, when sheet stacks of a job is stacked on the sheet stacking apparatus, sets the full state by conveying the sheet stacks to a position where the full-state sensor detects the full state.
 13. An image forming apparatus comprising a sheet stacking apparatus including a conveying unit that stacks sheet stacks while sequentially shifting the sheet stacks by a feed amount in a substantially horizontal direction; and a feed amount changing unit that, when the conveying unit stacks the sheet stacks, is configured to change the feed amount at a job transition point. 